As it is well-known, each color assembly or unit in a multicolor flexographic machine comprises a pair of cylinders, i.e. a screened and a cliché-carrying cylinder, respectively, that are parallel to one another and slidingly displaceable between a working position, in which the anilox or screened cylinder, i. e. an etched steel cylinder with a wide range of screen frames having from 3 to 200 lines per centimeter, is located in contact with the cliché-carrying cylinder positioned, in turn, in contact with a counterpressure or printing drum, and a rest position, in which the two cylinders are parallelly shifted or moved away from one another and from the counterpressure drum. Both screened and cliché-carrying cylinders have a hub member at each end thereof, which is designed to be mounted for rotation on a respective slide slidingly connected to, and supported by, a respective side of the support frame of a printing machine.
It has already been proposed, see Patent EP-1 199 167, how rotatably to support the hubs of a screened cylinder by means of a pair of cradle-shaped supports, to which a respective counter-cradle or cap member is articulated, that is angularly displaceable about a pin which is fixed to the cradle and has its longitudinal axis parallel to that of the cylinder, thereby obtaining a shape engagement with a portion of a respective hub of the cylinder supported for rotation in the cradle. Each cap member is angularly displaceable between a working position, where it is positioned abutting engagement with the cradle thereby rotatably holding the cylinder hub, and a rest position, where it opens upwards by rotating about its pin, thereby releasing the hub cylinder hub and allowing it to be removed or installed therein.
Such a solution, however, has some non-negligible drawbacks from the practical point of view. As a matter of fact, the use of a cap or counter-cradle system, also owing to the unavoidable presence of leverages operated by linear actuators, results in non-negligible clearances being created between hub and cradle-countercradle, which clearances affect the print quality at least in the long run.
It has already been also suggested—see ES-2 127 658—a method of replacing a cliché-carrying or anilox sleeve, such a method involving the following sequential operations:                detaching cylinders from counterpressure drum;        moving side counter-cradles away from their respective hub-carrying cradles of each cylinder;        displacing one hub-carrying cradle of the cylinder, so that the latter remains cantileverwise supported by its other hub-carrying cradle;        replacement of the sleeve;        return of hub-carrying cradle to a receiving position of the cylinder hub, i.e. to its starting position;        automatic or manual return of counter-cradle to its closed position on the cradle; and        return of cylinder (cliché-carrying or screened cylinder) to its working position in abutting engagement with the counter-pressure drum.        
During sleeve replacement and more precisely upon disengagement of one hub from the cradle, i.e. while the other cradle on the motor side of the printing machine entirely cantileverwise supports the cylinder, the cylinder weight can be considered to be a static load, which applies a bending moment to one of the cradles and its respective pad or bushing. With the lengths and the weight involved, the bending moment generated is always high and can deform the cradle and damage the (frustoconical) pad on which the hub rests.
With presently available technical solutions, some of which have been mentioned above, the operator is actively involved throughout the entire sleeve replacing procedure to carry out the hub disengagement/engagement and removing/laying operations in relation to the cradle after replacing the sleeve, once a sleeve has been replaced.
Another drawback of printing machines of the prior art in general is the use of rotary motors with motion transmission by means of ball screws for causing linear displacements of cliché-carrying and anilox cylinder supports away from or towards a counterpressure drum. As a matter of fact, as it is known to a person skilled in the art of the printing machines, such a cylinder handling system is responsible for considerable clearance, which in any case can cause printing inaccuracies greater than a hundredth of a millimeter that cannot be tolerated if a good print quality is to be obtained. Moreover, rotary motors are provided with circular encoders, which do not allow the exact position of the operated cylinders to be detected, whereby a reckoning algorithm is required in the electronic control unit of the printing machine.